As is well known, a number of sawing systems are used to produce boards from logs, including systems which provide for opening a log. The latter are referred to as being of a primary breakdown type. Most primary breakdown sawing systems have available various devices for automatically (e.g., electronically) measuring each log and for using these measurements to increase the rate at which logs are processed through the system--throughput, and/or for improving the value of lumber to be recovered from each log.
In order to achieve a high volume of lumber production, it is often desirable to first run each log through a primary breakdown saw to make a first planar cut, and after this is accomplished, to pass the resulting piece or pieces (slabs, cants, or flitches) through one or more resawing operations, the resawing operation being performed by the same or a separate saw. The resawing operation reduces larger pieces into common board thicknesses (e.g., four, eight inches, etc.); then, from the resawing operation, the resulting boards are passed through edgers (for width) and trimmers (for length) to achieve final board widths and lengths.
There are numerous choices available for sawing a log into lumber, and some are clearly better than others. Each log has unique geometry as to, for example, sweep, taper, notch (defects), length, and diameter. The amount of lumber recovered from a log is significantly effected by how these features are oriented to the plane of the primary breakdown saw cut. Thus, for maximum lumber recovery, there must be an initial determination of this plane before the cutting of it in order that the best opening planar cut in the log be made. In the trade, the term "best opening face" is employed to describe this cut. Once that opening face cut is made, the number of choices for sawing the remainder of the log are greatly limited, especially for small diameter logs. Thus, a slight error between an ideal opening face cut and an actual cut (e.g., resulting in an error on the order of .+-.1/8 to .+-.1/4 inch), may significantly reduce the amount of lumber yield from a log, particularly in the case of logs eight inches or smaller in diameter. It is to be appreciated that in order to determine a "best opening face," the log must first be measured, and with measurements, the log be analyzed, and thereafter, the position of a saw with respect to the log be set.
It is acknowledged that a variety of different sawing systems are presently used to produce boards from logs, including systems which provide for a separate opening of a log, as previously described. One well known primary cut system is referred to as a Head Rig and Carriage System. While refined to an extent over the years, the basic design of the Head Rig and Carriage System has been in use for the past 100 years. It employs a stationary band or circular saw with a track laid out parallel to this saw (Head Rig). The Carriage of this system is moved back and forth on these tracks past the Head Rig, with the Carriage having movable upright structures which move in generally horizontal guide ways, referred to as head-blocks. Logs are individually rolled onto the Carriage and are held against head-block knees by pointed clamps called dogs. A Carriage-borne log is positioned by using the head-blocks; the Carriage and log are then moved past the saw in successive passes to cut an initial face and then cut the log into acceptable board thicknesses. Electro-optical sensors may be used to measure the log after it has been dogged to the Carriage, and these measurements are then used to more intelligently position the log for cutting.
The Head Rig and Carriage System can cut accurately-sized lumber and can be designed to recover a high percentage of lumber from each log. The throughput of this type system is quite low, on the order of one to three logs per minute.
A second pertinent system is known as a Sharp Chain Primary Breakdown Saw. It employs a precision-guided chain having upwardly pointed teeth, with the chain being routed between a pair of vertical saws and/or chipper heads. Logs are placed on the Chain and conveyed through and past the saws or chipper heads. Sides of a log are removed by the saws (or chipper heads), leaving a center cant or two-sided log mounted to the Sharp Chain. The diameter of a log may be measured as the log is conveyed toward the saws, and these saws are moved toward or away from the Chain track in accordance with the measurements taken.
Since logs can be positioned on the Sharp Chain while the log is being sawn, the Sharp Chain System has a higher throughput, on the order of eight to ten logs per minute. However, this system provides a lower lumber recovery per log than the Head and Carriage System since a log cannot be repositioned once it is placed on the Sharp Chain. This means that if a log is initially improperly positioned, it will end up being improperly sawn. Since much of the scanning or log measurement with this type system is done after the log is placed on the track, the probability of improper placement and cutting and lumber waste is considerable.
The Sharp Chain System is more economical, and thus most competitive, when used to cut smaller and more uniform logs, such as are produced in northern forests, e.g., Scandanavia and Canada, while the Head Rig and Carriage System is best suited for larger diameter logs, decreasingly available in number from the Pacific Northwest.
Significantly, the lumber potential of the U.S. southeast is very substantial in both the short- and long-term future as this region contains an abundance of fast-growing, marketable pine timber. On the other hand, southern sawmilling has to date been generally inefficient and wasteful, with the waste wood simply being converted into chips for the paper industry. One reason for this has been that, in contrast to logs from the other regions mentioned, southern pine logs are generally irregular, with considerable sweep, taper, and diameter and length variations, as well as having knots and other defects. These irregularities and the limited volume (for footage) of lumber available in small diameter southern logs create a need for them not only to be individually analyzed before sawing, but also to be sawn accurately in terms of this analysis in order to recover their maximum value. Furthermore, and most importantly, these combined operations must be performed more rapidly than has heretofore been possible if the full potential utilizing southern pine logs for lumber is to be realized.
Accordingly, the object of this invention is to provide a primary breakdown sawing system which will accurately analyze and saw logs at a rapid rate and thus provide for improved economic recovery of lumber from available timber of varying size, large or small, and of varying quality.